In a circuit board, a SOC (system on chip), a pseudo SOC, or the like, on which a conventional digital/analog/RF mixed circuit is mounted, for example, there is the problem that errors are caused by mutual electromagnetic field interference between devices or noise propagating in GND (ground) or a power supply. To prevent such a problem, it is necessary to provide a wide space between devices. Therefore, it is difficult to reduce chip areas and mounting areas.
To reduce the space, a filter for preventing noise that propagates in the GND or the power supply and is in a frequency region harmful in circuit operation is used, for example. In this case, a filter for lowering the noise level in a limited frequency region, i.e. the cutoff region. The filter is formed with electronic components such as an inductor chip and a capacitor. Therefore, an increase in the number of electronic components is inevitable when the filter is mounted on a circuit board or the like.
In view of this, the use of an EBG (Electromagnetic Band Gap) structure in a dielectric substrate has been suggested, because the size of the circuit board or the like can be more effectively reduced with an EBG structure than with a filter formed with chip components. However, in a case where the cutoff band is set in a low frequency region (6 GHz or lower), the EBG structure becomes large, and the circuit board or the like cannot be made smaller.